1. Field of the Invention
This invention relates to a reverse speed shift device for a motor vehicle change-speed gearbox having a brake device actuated during the shift movement to brake an after-running gearbox shaft.
2. Description of the Prior Art
A reverse speed shift device, described in German Patent Application No. 23 36 250, operates to engage reverse drive gears during the preselection movement of the shift lever into the reverse shift plane. This movement loads a spring through a selector finger, which influences a selector fork mounted on the selector sleeve of the gearbox input shaft. The spring force skews the selector fork to brake the gearbox input shaft by operation of the increased friction force.
This reverse shift device has the advantage that braking of the afterrunning gearbox shaft is initiated during the preselection movement of the reverse speed. However, it has the disadvantage that the components necessary for the normal shift actuation are utilized as a brake device, with the result that they must be of complicated and costly construction.
It is customary in motor vehicle construction for a vehicle model to have engines of different capacities and correspondingly adapted clutches but substantially identical change-speed gearboxes. In many of the various engine-clutch gearbox combinations it has been discovered that scarcely any difficulties arise when an unsynchronized reverse speed is selected. However, with certain engine-clutch-gearbox combinations, particularly those in which the clutch plate has high inertia as a result of a longer after-running time of the connected gearbox shafts, difficulties in the form of disturbing grating noises are experienced when the driver attempts to engage the unsynchronized reverse speed during this after-running period.
Because the driver of a motor vehicle can only be expected to wait a brief period between disengaging a forward speed and engaging the reverse speed, it was necessary to find a solution to this problem that reduces this prolonged after-running time in a specific engine-clutch-gearbox combination.
A shift device disclosed in German patent application OS No. 28 09 915 discloses a friction device for braking a transmission shaft when a spring loaded toggle contacts the shaft. The toggle contacts a cylindrical portion of the shaft and is actuated by means of a spacer that engages a recess on a second shaft. The braking force is continuously applied and is removed only when the recess is removed from the spacer.